The leaders were to make their way to Ise Shima, a mountainous and sparsely populated area 300 kilometres (200 miles) southwest of Tokyo, whose mainly elderly residents rely chiefly on tourism and cultured pearls.
Security was tight across the region, with thousands of extra police drafted in to patrol train stations and ferry terminals, and to direct traffic on the usually quiet roads during the two-day meeting.
Tokyo said it was taking no chances in the wake of terror attacks that struck Paris and Brussels in recent months.
Obama says no apology for A-bomb on Hiroshima visit
Dustbins have been removed or sealed and coin-operated lockers blocked at train and subway stations in the capital and areas around the venue site.
Authorities said they will be keeping a close eye on so-called "soft targets" such as theatres and stadiums.
However, unlike in many other rich democracies, protests were unlikely to cause much of a security headache.
One demonstration organised for Wednesday morning attracted just a handful of largely elderly protesters.
Among the arrivals expected later Wednesday was Britain's David Cameron, whose country's referendum next month on continued membership of the European Union was likely to figure prominently on the summit agenda.
Cameron was set for a one-on-one meeting later in the day with summit host, Japanese Prime Minister Shinzo Abe.
Abe was also due Wednesday to meet US President Barack Obama, whose visit to the atomic-bombed city of Hiroshima on Friday threatened to overshadow the summit.
Obama will become the first sitting US leader to travel to the city, the site of the world's first nuclear attack on August 6, 1945.
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Obama has spent the last few days in Vietnam, where on Tuesday he urged the communist authorities to embrace human rights and abandon authoritarianism.
France's Francois Hollande and Germany's Angela Merkel were expected to arrive on Thursday morning. The meeting will also be joined by Italy's Matteo Renzi and Canada's Justin Trudeau.
The leaders will spend Thursday morning at Ise Jingu, a huge shrine complex that sits at the spiritual heart of Japan's native Shintoism.
In line with the animistic religion's traditions, the buildings are regularly replaced, but the shrine is believed to have occupied the same spot for more than 2,000 years.
The lacklustre global economy was expected to take centre stage in the formal talks which begin on Thursday afternoon, although divisions were likely to remain over whether the world should spend or save its way out of the current malaise.
Although China, the world's second largest economy, will not be present, it looks set to loom large over discussions, with Japan and the US keen to corral support for a growing pushback against Beijing's territorial assertiveness in the South China Sea.
The G7 will also discuss the spectre of Islamist terrorism, with France's Hollande keen to address the issue after a brutal year that saw France hit twice by jihadists.
Obama to make historic first presidential visit to Hiroshima
The imminent leaders' arrivals brought a measure of relief to members of the global press, who had spent much of Wednesday morning cooling their heels and interviewing each other.
Japanese television networks swarmed on foreign reporters in the cavernous press centre, demanding to know their impressions of this picturesque corner of the country, and desperate to hear what they thought of the lunch spread.
Journalists were treated to lavish displays of local specialities, from exquisite calligraphy performed with a special ink to photobooths that transformed users into ninjas -- the deadly black-clad assassins of Japan's feudal era.
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